Validation of MÉRA total precipitation at Stornoway (Scotland) with a 24 GHz micro rain radar: A Preliminary Investigation

Transcription

1 Validation of MÉRA total precipitation at Stornoway (Scotland) with a 24 GHz micro rain radar: A Preliminary Investigation Dr. Edward Graham 1 and Dr. Chris Kidd 2 1 University of the Highlands and Islands, Lews Castle, Stornoway, Scotland 2 NASA/GSFC, Greenbelt, MD 20771, USA 1

2 Where is University of the Highlands and Islands (UHI)? The Highlands and Islands Stornoway 2

3 The Highlands and Islands of Scotland 3

4 Stornoway 4

5 Quick overview of precipitation dynamics in Scotland Source: UK Met Office 5

6 Quick overview of precipitation dynamics in Scotland Sweeney and O Hare (1992): Geographical Variation in Precipitation Related to Lamb Circulation Types. Mayes (2000): Strong anti-correlation NW/SE UK. 6

7 The North Atlantic Oscillation (NAO) Stornoway Monthly Precipitation v NAO Pearson (r) correlation coefficients ( ) NCEP-NCAR Reanalysis (Kalnay et al. 1996) November 0.57 December 0.72 January 0.74 February 0.75 March

8 Quick overview of precipitation dynamics in Scotland 8 Source: NASA Terra

9 Quick overview of precipitation dynamics in Scotland SNIFFER (2006), Changes in precipitation 1961 to 2005 Stornoway Airport ( ) to ( ): Jan: 22% Feb: 27% Mar: 11% Apr: 14% Annual: 7% Graham, 2012) Overall UK precip increase of 5-6% from to (same as in Ireland; Dwyer 2012, Gleeson et al. 2013) 9

10 The Stornoway 24Ghz micro rain radar (LE-Radar) Motivation: NASA Global Precipitation Mission Operates continuously in FM mode at 24GHz with saw tooth signal Vertical pulse of radiation, back-scattered (reflected) by hydrometeors (snow, hail, sleet, rain) and possibly aerosols Vertical resolution of 30m x 100 steps, maximum height penetration 3100m. Data averaged over time bins of 1min As λ (1.3cm) > drop size, then amount of back scatter to 6 th power of the drop radius Bright band / fall velocity / Doppler shift determined from reflection & est. drop spectrum. Very high spatial/temp resolution Can detect low-tropospheric light drizzle which conventional PPI radar can t 10

11 The Stornoway 24Ghz micro rain radar (LE-Radar) Installed 15 June 2015! No shortage of rain during summer 2015 or most other times! 3 x other rain gauges within ~1.5km (SEPA, my own x 2) 11

12 Example 4-panel graphical output Raw reflectivity values(measured in dbz): Anything above 35 dbz is heavy precipitation (~65dbZ = large hail) Bright Band visible Rainfall rate (mm/hr): Anything above 0.2mm/hr will wet the ground, above 1mm/hr will make puddles, 10mm/hr is a downpour. Fall velocity (speed of descent of rain/snow): The largest raindrops fall at 6-8m/sec, snowflakes ~2m/sec, graupel 3-4m/sec Doppler Velocity (m/sec): Essentially the same as fall velocity, in a nonmoving frame of reference (relative to the radar) 12

13 Example Event 1: Low-Level Drizzle Stratus drizzle ( smirs ) missed by conventional PPI radar in M T airflows 13

14 Example Event 2: #StormFrank Dec

15 Example Event 2: #StormFrank Dec 2015 Left: 00z 29 Dec 2015 / Right: 00z 30 Dec

16 Example Event 3: Convective Boundary Layer A fine, warm summer s day 16

17 A Case Study: MRR, MÉRA and Met Office PPI radar: 30 June 2015 MRR total precip: 20.0mm, 20.9mm at 200m, 300m above MRR 17

18 Met Office Radar (PPI zoom): 30 June 2015 Met Office Rain Radar data from the NIMROD System; NCAS, BADC. Total Met Office PPI precip (Stornoway): ~15-20mm 3 x rain gauges (within ~1.5km): 18.6mm, 18.4mm, 19.0mm 18

19 Case Study: MÉRA, 30 June 2015, 00-06z 19

20 Case Study: MÉRA, 30 June 2015, 06-12z 20

21 Case Study: MÉRA, 30 June 2015, 12-18z MÉRA Stornoway Point total: 6.9mm (but Isle max: 20.5mm) 21

22 A Case Study: MRR, MÉRA and Met Office PPI radar: 30 June 2015 Simple 1-day quantitative summary DATA SOURCE MÉRA Stornoway (single point only): MÉRA (island max): Micro rain radar (MRR): Rain gauge #1: Rain gauge #2: Rain gauge #3: PRECIP AMOUNT (24hr) 6.9mm 20.5mm 20.0 to 20.9mm 18.4mm 18.6mm 19.0mm Lower rain gauge totals easily accounted for by wind loss / spashing / higher altitude of MRR estimate Possible edge effects? (as on northern boundary of MÉRA) 22

23 Summary / Conclusions Significant precipitation changes are afoot in NW Scotland. The Stornoway MRR with MÉRA offer new research opportunities Precipitation is largely stochastic mesoscale phenomenon -> longer time series needed for a comprehensive climatological analysis and validation Inadvertent complex choice of 30/6/2015, as front had localised embedded convective precip -> need full MÉRA precipitation please! Direct assimilation of very high resolution radar into models might continue to pose complications (e.g. PWV by GNSS, Guerova et al. 2004) Possibility of separate MÉRA geopotential paper in Weather re: Extreme thin thicknesses during recent #BeastfromtheEast 23

24 Thank you! 24

25 Appendix Stratus drizzle (smirs) missed by conventional Met Office PPI radar in M T airflows E. Graham et al.,

26 Precip Radar 30 Jan 2018: Source: UK Met Office Quick overview of precipitation dynamics in Scotland 26

27 The North Atlantic Oscillation (NAO) Hurrell (2003), NCAR; Osborn (2011) 27

28 30 June 2015: Synoptic Charts 28

29 30 June 2015: Synoptic Charts 29

30 30 June 2015: Synoptic Charts 30

31 30 June 2015: Synoptic Charts 31